In the past, there was a clear distinction between telecommunication and data communication networks. Telecommunication networks, such as Public Switched Telephone Networks (PSTN) and Public Land Mobile Networks (PLMN) carry voice and data over circuit-switched connections, where the ‘circuit’, e.g. a time slot in a wireless connection or a digital transmission line, is reserved for the voice or data call for the whole duration of the call, even during idle periods, i.e. when there is no voice or data to transmit.
Data communication networks, on the other hand, typically carry data over packet-switched connections, where network resources are reserved for a particular session only when there is data to be transmitted. When the session is idle, network resources are allocated to carrying data for other, active sessions. A vast majority of today's data communication networks are based on protocols that utilize the TCP/IP protocol stack. An example of such network is the Internet, which in today's language may refer to any one of a number of different networks implemented with different protocols, such as the Wold Wide Web (HTTP) or Usenet (NNTP).
Recently, technical development has been leading towards convergence of telecommunication and data communication networks, which means in general that both telecommunication and data communication applications use the same physical and/or logical network for carrying voice and data. This trend has many advantages both from a network operator's and a consumer's point of view. For example, a network operator needs to invest in and maintain only one physical network in stead of two parallel networks for telecommunication and data communication traffic, respectively. This reduces capital, operating, and maintenance expenses that the operators incur, which in turn should bring about lower call and data transfer rates for subscribers. In some countries this convergence of tele-communication and data communication may be slowed down by pricing policies of the network operators, which they may use to safeguard return on their past investments in telecommunication infrastructure.
In a network that is built to carry both telecommunication and data communication traffic, arranging the communication according to a packet-switched scheme is an advantageous design choice, as at least in theory serving the same amount of subscribers requires less capacity in a packet-switched network than in a circuit-switched network. This is due to the above mentioned fact that in packet-switched networks, a session consumes network resources only when there are data packets to be transmitted, and during idle periods the network resources are available for other sessions.
As already mentioned, TCP/IP-based networks are nowadays the prevailing type of packet-switched networks. Methods and protocols have been developed for carrying voice over IP networks so that the IP networks are capable of providing voice communication services. Schemes for carrying voice over IP networks are commonly referred to as Voice over IP or VoIP. With the advent of VoIP services and applications, consumers have been able to use their home computers as voice communication devices and make phone calls over their Internet connections at relatively low flat rates.
VoIP calls are also available over Wireless Local Area Network (WLAN) connections, and along with introduction of dual-mode or multi-mode mobile phones, which are equipped with hardware and software for connecting the phone to a WLAN network, the option for making a VoIP call perhaps at a lower rate as compared to that of e.g. a GSM call rate has become available also for mobile phone users.
Making a VoIP/Internet call from a mobile phone at a flat rate may require that the call is a VoIP call end-to-end, i.e. both parties of the call are available for a VoIP call. For example, if a calling party is available for a VoIP service, but the called party is not within a VoIP service area, the call may e.g. be transmitted through a VoIP gateway to and terminate in a GSM network, and the GSM leg of the call may be charged at a rate set by the GSM operator, which may negate the benefit of the flat rate of the VoIP leg of the call.
It would therefore be useful if the calling party knew before making a VoIP call or initiating another type of connection, whether the called party were available for the VoIP call or the other type of communication. Obviously, the calling party could contact the called party by other means, e.g. by making a telephone call through GSM or fixed line service, before trying to make a VoIP call to check that the called party is actually within a VoIP service area, but it is inconvenient to first make e.g. a GSM call and then the VoIP call, possibly dialling both telephone numbers by means of the mobile phone keypad, and at least one party of the call incurs the cost of the GSM call.
It is an object of the present invention to eliminate or at least alleviate the above described inconveniences.